I use one of these atv-towed flail mowers. It is the very old design that Jack noted above. I bought it from Bestco because everyone else was out of stock.
It works (so far) but has numerous design and manufacturing defects.
There is an opportunity for a better engineered self-powered flail mower. I've seen some in Europe but not in the U.S.A.- yet .
1. Center the engine so the machine doesn't have a disproportionate amount of weight on just one side.At least move the battery and gas tank to the other side. A problem on hillsides.
2.Offer an adjustable "Walking Beam" or other tandem 4 wheel design to be more stable on rough/sloped land.Offer an option that allows better adjustment of tongue weight.
3. Provide a remote stop/start control - it's just a cable and a switch !
4. Use a drive belt that is 'cogged' and segmented- like a Bobcat drive belt.
5. Use waterproof engine wiring connectors instead of exposed ,naked ones.
6. Come up with an alternative to the anti-scalp roller at the rear. At least center and secure the bearings positively and have a center support bearing/bracket in the middle.!
7. Offer larger diameter tires and easier height adjustment to help with rough terrain.
8. Offer a diesel powered alternative because gasoline is a greater fire risk and most other farm machines are diesel now.
9. Simplify in-field adjustments/repairs by standardizing fastener sizes. Mine has 15,16,1718,19 mm and more arbitrarily scattered around the machine.Reposition the turnbuckle so it is not buried beneath the drawbar. Use a tapered pin on the drawbar to make adjustments in the field easier.
10. Offer a front mounted brush bar instead of relying on the sheet metal to knock over thicker plants.
11. Option to reposition wheels to the rear to allow mowing closer to fences/walls/trees
12. Make all grease zerks accessible !!
13. Provide a clutch+lever to manually disengage the flail rotor from the engine.
I have more suggestions but you get the idea ? This design is way overdue for improvement. Simply copying what the Europeans have had for years already would be a good start.And few of theses improvements are expensive. I hope this inspires some enterprising manufacturer to try harder.